1. Field of the Invention
This invention relates to a rare-earth element/cobalt-type magnet powder for resin magnets having a specific composition, that is, a samarium(Sm)/cobalt(Co)-type magnet powder that includes praseodymium(Pr) and neodymium(Nd) added in.
2. Description of the Prior Art
Rare-earth element/cobalt type magnet powders (hereinafter referred to simply as "magnet powder"), particularly samarium/cobalt-type magnet powders, have been used, in combination with resins such as polyamide, for the manufacture of resinous magnets which are employed in various types of motors, electrical appliances, computer terminal equipment and many other products.
Two methods are known for commercial production of magnet powder: the melt process, in which component metals are melted in a high-frequency furnace or in an arc furnace, then the molten alloy is cast into a mold to form ingots, and finally by pulverization; and the reduction-diffusion process, in which a mixture of rare-earth metal oxides, a reducing agent, such as calcium metal, and cobalt powder are placed in a vessel and heated to a temperature in the range of 900.degree. to 1100.degree. C. under normal pressure in an inert gas atmosphere, then reaction product is put into water to form a slurry, and then the slurry is treated with water and a dilute acid.
The magnet powder obtained by the melt process has low residual mangnetic flux density, although high in coercive force. On the other hand, the reaction products of the reduction-diffusion process have (1-5) phase composition on average (actually multi-phases). Hence, the magnet powder obtained by this process, for use as a sintered magnet, is heat-treated, after being press-formed, to enhance its magnetic characteristics. Since such heat-treatment cannot be performed after the magnet powder is kneaded with a resin, the resultant resin magnet shows far poorer magnetic characteristics, particularly in residual magnetic flux density.